Removes unused variable
Removes inheritance JavaClass<JavaInstance

This will break at some point.
Creates wrappers through PyObject_CallObject

JavaClass and JavaInstance objects are now created through
PyObject_CallObject() instead of simply PyObject_New.

PyObject_NewVar() was kept for the methods (BoundMethod, UnboundMethod,
ClassMethod) as the need to pass the size around would only add
unnecessary code.